/**
 * abc 旋转词
 *      bca
 *      cab
 */
console.log(isRotation('abc','bca'));
 function isRotation(a,b){
     if(a===null||b===null||a.length!==b.length){
         return false;
     }
     let sumStr = b+b;
     return sumStr.indexOf(b)!==-1;
 }